Exhaust Back Pressure Regulator (EPR)

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

M: Exhaust Back Pressure Regulator (EPR)

M: Introduction

M1 DIAGNOSTIC TROUBLE CODE (DTC) P0475: CHECK FOR GROUND IN CIRCUIT 574 (BK/PK). DTC P0475 INDICATES THAT A CIRCUIT FAILURE HAS OCCURRED IN THE EBP CONTROL SOLENOID CIRCUIT

possible causes:

shorted to power
open/grounded circuit
damaged solenoid
damaged PCM

Disconnect EPR harness.
Key off.
Measure resistance between Pin A and ground.

Is the resistance less than 5 ohms?

Yes	No
GO to M2.	SERVICE open in Circuit 574 (BK/PK). RERUN Scan Tool Diagnostic Test.

M2 CHECK EPR COIL

Measure resistance across EPR coil contacts A and B.

Is the coil resistance between 2.5 ohms and 12 ohms?

Yes	No
GO to M3.	REPLACE regulator. RERUN Scan Tool Diagnostic Test.

M3 CHECK FOR SHORT TO POWER IN CIRCUIT 318 (GY/R).

Disconnect PCM. Inspect terminals for damage or corrosion, service as required.
Measure voltage between Pin B and ground.
Shake harness.

Is B+ ever present?

Yes	No
SERVICE short to power in Circuit 318 (GY/R). RERUN Scan Tool Diagnostic Test.	GO to M4.

M4 CHECK CIRCUIT 318 (GY/R) FOR SHORT TO GROUND

PCM disconnected.
EPR disconnected.
Measure resistance between Pin B and ground.
Shake harness.

Does the resistance ever drop below 10,000 ohms?

Yes	No
SERVICE short to ground in Circuit 318 (GY/R). RERUN Scan Tool Diagnostic Test.	GO to M5.

M5 CHECK FOR OPEN IN CIRCUIT 318 (GY/R)

PCM disconnected.
EPR disconnected.
Install breakout box.
Measure resistance between Pin B and Test Pin 42.
Shake harness.

Does resistance ever go above 5 ohms?

Yes	No
SERVICE open in Circuit 318 (GY/R). RERUN Scan Tool Diagnostic Test.	GO to M6.

M6 PERFORM OUTPUT STATE CHECK

Disconnect EPR.
Attach NGS Tester.
Key on, engine off.
Measure voltage between EBP connector harness side Pin B and chassis ground.
Run KOEO Output State Test on NGS Tester.

Does voltage toggle between 12v and 0v?

Yes	No
Fault is intermittent, unable to duplicate failure.	REPLACE PCM.

M7 KOER DIAGNOSTIC TROUBLE CODE (DTC) P0476

DTC P0476 indicates an exhaust back pressure control valve performance malfunction was detected during KOER On-Demand Self Test.
Possible causes:

stuck or damaged butterfly
misadjusted or damaged linkage
restricted exhaust
exhaust leaks
damaged PCM
EPR valve
EBP sensor

If KOEO EBP faults are present, repair them before continuing.
Visually inspect butterfly tang (refer to Section 4C, Diagnostic Routines, Performance Diagnostic Procedures, Exhaust Restriction for exhaust back pressure regulator tang position illustration.

Is tang in the open position?

Yes	No
GO to M8.	REPAIR condition causing valve to be stuck closed.

M8 EXHAUST RESTRICTION CHECK

NGS Tester installed.
Select EBP PID from the PID/DATA monitor menu on NGS Tester.
Engine running.
Accelerate engine to WOT and hold for 30 seconds.

Is EBP below 28 psi?

Yes	No
GO to M9.	REPAIR restricted exhaust condition. CLEAR DTC and RETEST.

M9 EBP SENSOR CHECK

NGS Tester installed.
Select EBP PID from the PID/DATA monitor menu on NGS Tester.
Engine running.
Record EBP valve.
Accelerate engine several times.

Does EBP increase at least 4 psi with acceleration?

Yes	No
M10.	REPLACE EBP sensor. RETEST system.

M10 INSPECT FOR EXHAUST LEAKS

Inspect turbo pipe, crossover pipes and exhaust manifolds for leaks.

Are exhaust leaks present?

Yes	No
REPAIR exhaust leak. CLEAR DTCs and RETEST.	GO to M11.

M11 EBP CHECK DURING KOER

Key off.
Disconnect EBP sensor connector.
Inspect for damaged or pushed out pins, loose wires or corrosion. Service as necessary.
Install ICP/EBP Adapter Cable D94T-50-A or equivalent between EBP sensor and vehicle harness.
Measure voltage between signal circuit and signal ground on ICP/EBP Adapter Cable D94T-50-A or equivalent.
Perform KOER On-Demand Self Test.

Does voltage increase 2.0v ± 0.5 and then decrease as the test ends?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	GO to M12.

M12 EPR VISUAL INSPECTION

Observe EPR valve linkage while performing KOER On-Demand Self Test.

Does the linkage move during the test?

Yes	No
CHECK EPR linkage adjustment. REFER to the Powertrain/Engine Group in the Service Manual. RETEST system.	REPLACE EPR valve. CLEAR DTCs and RETEST.